Childhood asthma affects roughly 10 million children under age 16 in the United States. Reduced early life exposure to microbial products, particularly endotoxin, has been proposed as an important factor which may account for increased risk of asthma through increased risk of allergy or of allergic lung inflammation. Low asthma rates observed in farm children has lent credence to this hygiene hypothesis. However, endotoxin is also associated with occupational airways inflammation, increased asthma morbidity, and wheeze in infants. The different influences of endotoxin on asthma development and exacerbation can only be clarified by prospective studies. Our current project, ES07036-05, is examining whether endotoxin and related microbial exposures reduce risk of developing asthma in a birth cohort of 505 Boston area children. With this supplement, we propose to increase our power to test the hygiene hypothesis by measuring endotoxin and related microbially derived exposures (lipopolysacchande (LPS), peptidoglycan (PG), total fungal biomass, and (1 -3)-Beta-D-glucan) for 1,002 children in the Yale Childhood Asthma Study birth cohort with 41 percent minority (Black and Hispanic) members. The Yale study also includes 1,002 older siblings with doctor-diagnosed asthma for whom we will prospectively determine whether microbial exposures increase asthma morbidity. The proposed expanded study population has significantly different hereditary and environmental influences than the Boston cohort. This supplement will provide sufficient numbers of subjects and statistical power to achieve the following objectives: (1) test the hygiene hypothesis in Black and Hispanic (mainly Puerto Rican) children; (2) determine the effect of endotoxin and other key microbial exposures on asthma morbidity in minority children; and (3) set the stage for future studies of gene-environment interactions between polymorphisms in the pattern receptors for innate immunity and endotoxin and other microbially derived exposures recognized by these receptors. Analyses will be controlled for both allergen exposure and a wide range of other demographic and environmental factors using data collected by the Yale study. This application requests funds for endotoxin, LPS, PG. fungal biomass (ergosterol) and (1 -3)-Beta-D-glucan assay of settled dust and for data analysis and interpretation. This supplement will be one of the first opportunities to test the hygiene hypothesis in a large minority population